Piezoelectric relay



Feb- 25, 1969 R. voN roMKEwlTscl-l ETAL. 3,430,020

PIEZOELECTRIG RELAY Filed Aug. 17. 196e da mi@ ATTYS.

United States Patent 3,430,020 PIEZOELECTRIC RELAY Romuald vonTomkewitsch, Ebenhausen, and Werner Busch, Munich, Germany, assignors toy Siemens Aktiengesellschaft, a corporation of Germany Filed Aug. 17,1966, Ser. No. 573,072 Claims priority, application 9(irrmany, Sept. 20,1965,

U.s. c1. o- 131 1o claims 1m. c1. H01h 57/00 ABSTRACT OF THE DISCLOSUREIt is known to utilize the piezoelectric effect of certain crystals inthe construction of relays. If a voltage is applied to such a crystal,of plate formation, a bending throughout of the plate results, and bymeans thereof a contact assembly associated with such plate may beactuated. Because of this manner of operation, crystal plates of thiskind are often called bending vibrators.

The advantage of relays with piezoelectric excitation consists, aboveall, in the fact that they possess a high electro-mechanical degree ofefliciency and that the initial frequency is considerably higher thanthat of electromagnetic relays. Furthermore, as no electro-magneticsystem is necessary for the operation of such a relay, neither an ironcore nor a winding is required for the structure, and as the voltagesource of a piezoelectric relay is drawn upon only in a capacitivemanner only a very small power requirement is necessary for theexcitation.

In spite of these qualities, particularly favorable for the constructionof miniature relays, piezoelectric relays thus far have had littlesuccess in the field. This fact is attributed to the fact that therequired crystal plates are, according to their nature, only suitable-for small operating travel, andr correspondingly a large mechanicalleverage is required for obtaining the contact operation necessary forpositive relay operation. For this reason relatively long and thinbending vibrators or appropriate lever transmission means for obtainingthe necessary contact travel have been necessary. The first mentionedsolution has the disadvantage that a relay of this type is notsulliciently sturdy. On the other hand, lever transmissions usuallyrequire a large number of moving parts which are bound to operate withlosses which are not negligible and cannot be disregarded.

The disadvantage of known piezoelectric relays above discussed indetail, are avoided according to the invention by the feature that abending vibrator, preferably of circular conliguration, is provided witha pressure chamber to which a metering tube enclosing a mercury drop isconnected, and during excitation and resulting bending of the vibrator,the contact gap located in the metering tube may be closed by themercury drop. In this case the power-way transformation is effected bymeans of the mercury located in -the metering tube almost without loss.More important, no lever transmissions are required, so that resultingmechanical losses are substantially elimi- ICC nated. If, in this case,the metering tube selected is appropriately narrow, the mercury drop tobe accelerated during excitation of the relay likewise may be relativelysmall.

In order to achieve relay operation in a manner largely independent ofposition and temperature, in a particularly suitable ydevelopment of theinvention there is provided the feature that the pressure chamber whichencloses the bending vibrator is divided into two cooperative chambersand that metering tube or passageway, provided with the mercury drop,preferably formed by a central bore in the bending vibrator, effects apressure compensation during excitation of the bending vibrator andtherewith the bridging-over of the contact gap. In this case the dividedpressure chamber is expediently filled with a liquid which is notelectrically conductive, for which purpose, for example, alcohol orthin-flowing oil are suitable. Because of the division of the pressurechamber, arranged symmetrically on opposite sides of the vibrator asimple temperature compensation is assured.

If the vibrator during excitation in accordance with the operationeffect a bending movement, the volume of one of the pressure chamberdivisions is reduced and the volume of the other pressure chamberdivision is enlarged. Since the fluid compensation can take place onlythrough the metering passageway (central bore), a mercury drop thereinis shifted from one tube end to the other. The result of this movementis, for example, that one pair in the metering passageway is openedwhile a second contact pair is closed.

In order to increase the operating dependability of such an arrangement,it is advantageous to attach a fine mesh screen to each end of themetering passageway which, for the fluid, presents little mechanicalresistance, but for the mercury drop, presents a high resistance. Themercury drop is thereby prevented from leaving the metering passagewayif not too great an electrical over-excitation of the bending vibratorexists. It is even more effective to lengthen the metering passagewaytowards both ends in the form of capillaries whereby, due to thecapillary action, the mercury cannot flow out of the meteringpassageway.

An especially advantageous construction for the prevention of a ow ofmercury out of the metering passageway provides spherical bulges in themetering passageway at the contact gaps. The surface tension of themercury, as is well known, is so large that in this case the mercurydrop cannot leave the measuring passageway even if the relay is mountedhorizontally. In order to obtain a maximum operating dependability, afurther embodiment of the invention is so constructed that the meteringpassageway with its spherical bulges, includes a separate pressurechamber disposed at both sides of the bending vibra-tor. In this manner,the fluid pressure resulting during an overexcitation is blocked so thatthe mercury drop cannot leave the metering passageway and thus thecontact gap. Expediently the membranes therefore are constructed asresilient members of plate-like conliguration. Such resilient membersalso have the effect of energy storage means and gives the relay a snapaction characteristic which is effective in the achievement of anacceleration of the switching operation.

In order for the temperature compensation previously mentioned to alsooperate effectively, it is advantageous to provide a capillary throughthe bending vibrator conn ecting the two divisions of the pressurechamber, through which a gradual pressure compensation may take place atany time. The operation of the relay, with an `appropriate proportioningof the capillaries, is not operatively impaired as the supplementalcapillary olers a relatively high resistance to the sudden pressureincrease during excitation of the relay. In order to further improve thetemperature compensation and to firmly anchor the connections to theoperative contacts, the elements of the relay can be assembled into aunitary construction and such unit encased in suitable material.

Further details of the invention are evident from the subsequentdescription of several examples of construction and the drawings,wherein like reference characters indicate like or corresponding parts,and in which:

FIG. 1 is a sectional view, taken approximately on a central verticalline of FIG. 2, illustrating an embodiment of the invention;

FIG. 2 is a sectional view taken approximately on the line A-B of FIG.1;

FIG. 3 is a sectional view, similar to FIG. l, illustrating a modifiedconstruction; and

FIG. 4 is a schematic figure illustrating a further modification of theinvention.

FIGS. 1 and 2 schematically illustrate a piezo-electric relay, whichcomprises a circular bending vibrator member 1 with a central boretherein which serves as a metering passageway 3 for a drop 4 of mercurydisposed therein. The bending vibrator 1 is enclosed on both sides by apressure chamber divided into two sections or divisions 2 in which anon-conductive fluid is disposed. Because of this dual arrangement ofthe pressure chamber symmetrically to the vibrator 1, a largetemperature compensation is assured. If the vibrator 1 bends axiallyduring excitation, as indicated in FIG. 1 by the arrows, the volume ofone chamber is reduced and the volume of the other chamber is enlarged,with the fluid compensation taking place through the metering passagewaywhereby the mercury drop therein is shifted from the right side to theleft side. By this process, the contact gap Sa/Sb is operatively openedand the contact gap Srl/5b' is operatively closed. In order -to preventthe mercury drop 4 from being discharged from the metering passageway 3,fine mesh screens 6 are arranged at both ends of the metering passagewaywhich offer a high resistance to the passage ofthe me-rcury.

In order to obtain an especially high security against the discharge ofthe mercury drop from the metering passageway, especially if the relayis overexcited, an improved relay construction may be employed, such asthat illustrated schematically in FIG. 3. It should 'be particularlynoted that in this embodiment the metering passageway 3 possessesspherical bulges or enlargements at the contact gaps Sa/Sb and 5a'/5b.These spherical bulges are connected with each other by only a narrowcentral passageway, as a result of which the mercury drop 4 cannot dropdownwardly through such center passageway, even if the relay ishorizontally mounted, because the drop always seeks to occupy aspherical form due to its great surface tension. Membranes 7a and 7b areadditionally provided at the ends of the metering tube to also restrictthe uid pressure therebehind during the occurrence of `an over actuationand excessive exing. As a result, the mercury drop 4 is restricted inthe metering passageway and therewith the contact position existingunder any circumstances. The membranes illustrated in this tigure areconstructed as plate-like springs and since they have an energy storageeiect, they have a more or less snap action, which may be epeciallyadvantageous if the excitation alteration, i.e., the pressure alterationinvolved takes a slow course since in this manner, the switch-overaction is necessarily accelerated.

It has already been mentioned that due to the symmetrical arrangement ofthe two-section pressure chamber 2, exceptionally eilicient temperaturecompensation may be obtained. However, this temperature compensationapproaches an optimum only when the volume of the two sections of thepressure chamber, as well as the heating and the mechanical stiffness ofthe closure members 9 are equal. Since such an equality may, from thestandpoint of manufacturing technique, be obtained only with diiculties,a very line bore 8 is additionally provided between the two chambersections as a compensation capillary over which pressure compensationmay gradually take place.

In practice, it may occur that in order to prevent a possible inuencingof the bending vibrator, in particular where higher voltages areinvolved at the switch contacts, a separation of the excitation portionand the .contact portion of the piezoelectric relay is desirable. InFIG. 4 a possible form of construction is schematically illustrated, inwhich letters have been employed as reference characters. Thisembodiment comprises a bending vibrator B and a resilient metal plate Mwhich takes the place of a second bending vibrator which would otherwisebe required at this side. In this case the insulation means I which may,for example, be produced out of ceramic, serves as the contact carrier.The mercury drop Q is disposed in the metering tube in a manner similarto that illustrated in FIG. l, with the mercury drop being retained inthe connection branch between the two-section pressure chamber D whichis lfilled with fluid. The common contact lead is designated by thereference letter K.

Changes may be made within the scope and spirit of the appended claimswhich define what is believed to be new and desired to have protected byLetters Patent.

We claim:

1. A piezoelectric relay, comprising a Ibending vibrator member of asolid piezoelectric material, means `cooperable with said vibratormember for-ming a pressure chamber at each side of said vibrator member,with the latter forming a dividing wall therebetween, the volumes ofwhich may be altered by excitation of said vibrator member, an elongatedmetering passageway extending through said member operatively connectingsaid pressure chambers, a drop mercury disposed in said passageway,contact means disposed in said metering passageway cooperable with saidmercury, whereby the latter, in one position in the passageway isoperable to connect said contacts, and when in another position in saidpassageway an inert iiuid disposed in both said chambers operative totransmit pressure changes therein, responsive to alterations in thevolumes of said chambers, to said mercury drop for effecting movement ofthe latter in said passageway.

2. A piezoelectric relay according to claim 1, wherein said vibrator isin the form of a circular disk and said metering passageway is centeredtherein.

3. A piezoelectric relay according to claim 1, wherein an electricallynon-conductive fluid is disposed in the respective chambers.

4. A piezoelectric relay according to claim 1, comprising in furthercombination, a ne mesh screen disposed at each end of said meteringpassageway, which, for said uid, represents an insignificant mechanicalresistance, 1but a large resistance for said mercury drop, to restrictmovement of the latter out of the ends of said passageway.

5. A piezoelectric relay according to claim 1, wherein the effectivecross sectional area of said metering passageway, at the ends thereof,is less than at an intermediate portion of the passageway.

6. A piezoelectric relay, comprising a bending vibrator, means`cooperable with said vibrator forming a pressure chamber the volume ofwhich may be altered by excitation of said vibrator, a meteringpassageway operatively connected with said pressure chamber, a drop ofmercury disposed in said passageway, contact means disposed in saidmetering passageway cooperable with said mercury, whereby the latter, inone position in the passageway is operable to connect said contacts, andwhen in another position in said passageway is operable to open saidcontacts, and a fluid disposed in said chamber operative to transmitpressure changes therein, responsive to alterations in the volume ofsaid chamber, to said mercury drop for eiecting movement of the latterin said passageways, said pressure chamber being divided into twosections, between which the bending vibrator is disposed, said meteringpassageway operatively extending between such sections for effecting apressure compensation therebetween during excitation of the vibrator,and movement of said mercury drop as a result thereof, means foroperatively separating the metering passageway and with respect to thefluid in said pressure chamber, in the form of respective membranesdisposed at opposite sides of the vibrator.

7. A piezoelectric relay according to claim 1, comprising in furthercombination, a capillary port, formed by an opening in said vibrator,which provides a slow pressure compensation of any static pressuredifferential between the two pressure chambers.

8. A piezoelectric relay according to claim 1, wherein the constructioncomponents of the relay are assembled into a unitary structure, and amass of sealing material in which said structure is encased, forpromoting an improvement in temperature compensation and anchorage ofthe connections to said relay contacts.

9. A piezoelectric relay, comprising a bending vibrator, meanscooperable with said vibrator forming a pressure chamber the volume ofwhich may be `altered by excitation of said vibrator metering passagewayoperatively connected with said pressure chamber, a drop of mercurydisposed in said passageway, contact means disposed in said meteringpassageway cooperable with said mercur-y, whereby the latter, in oneposition in the passageway is operable to connect said contacts, andwhen in another position in said passageway is operable to open saidcontacts, and a fluid disposed in said chamber operative to transmitpressure `changes therein, responsive to alterations in the volume ofsaid chamber to said mercury drop for eiecting movement of the latter insaid passageways said pressure chamber being divided into two sections,between which the bending vibrator is disposed, said meteringpassageways operatively extending between such sections for effecting apressure compensation therebetween during excitaiton of the vibrator,and movement of said mercury drop as a result thereof, the interior ofsaid metering passageway being provided with enlargements of sphericalconfiguration, disposed to contain said drop of mercury when it is inits respective operative contact closing and contact opening positions.

10. A piezoelectric relay according to claim 6, wherein said membranesare constructed as spring members of plate-like formation.

References Cited UNITED STATES PATENTS 2,203,332 6/1940 Kinsley 20G-181XR 2,851,618 9/1958 Krawinkel 200-181 XR 2,883,486 4/1959 Mason 20G-181ROBERT K. SCHAEFER, Primary Examiner.

H. BURKS, Assistant Examiner.

